Research On Impact Energy Measurement Based On Fiber Bragg Grating Edge Filter Method And Damping Attenuation

A two-stage real-time demodulation based on the principle of fiber Bragg grating(FBG)edge filtering is used to measure different impact energy in this paper.According to the basic theory of FBG edge filtering,when the impact energy is weak,we make the narrow line-width laser as a stationary probe and utilize the edge moving of FBG reflection spectrum to demodulate based on the different optical power reflect characteristics.When the impact energy is stronger,we research on the relationship between the attenuation time and the impact energy according to the plates with different damping coefficient.This paper has the following innovations:First,we designed a method to demodulate the low-speed impact energy without using spectrometer to measure the center wavelength of FBG in real time.We replace the broadband light source used in the traditional edge filtering method by the narrow line-width laser,and utilize the self reflective spectral edge of the Bragg fiber grating as the filter,which can greatly improves the sensitivity of the impact energy demodulation.Second,based on the relationship between the attenuation time and the forced vibration energy,a demodulation method for solving the moving limit of center wavelength of FBG is proposed and verified by the design of experiments.The work and experimental results of this paper are as follows:In Chapter 1,we describe the development of FBG sensing technology.Starting from the traditional application of FBG,we show the significance of impact energy measurement and the progress of this research at home and abroad.In Chapter 2,we introduce the history of fiber grating discovery,the technology of writing,the classical theory,and the application of sensing.The simulation of FBG,LPFG and cascaded FBG is carried out by MATLAB software.In Chapter 3,we focus on the development of FBG demodulation technology,including matched filtering,F-P filtering and tunable light source.At last,the edge filtering demodulation technology which we will focus on is introduced.In Chapter 4,a new scheme of impulse energy measurement based on edge filtering and demodulation is described.For the impact process of sphere acting on aluminium plate,the rightedge moving filter demodulation method of FBG spectrum is used in the experiment.The experimental results show that in the range of 1-16 g,when the energy is low,the highest fitting degree is 0.988,the highest sensitivity is 7.476mv/g,and the fitting degree and sensitivity are good by using the reverse edge filtering demodulation method.In Chapter 5,a scheme of demodulating impulse energy based on damping attenuation principle is described.For the impact process of 10-90 g sphere acting on acrylic(PMMA)and aluminium plate,a new demodulation method based on damping attenuation principle is proposed.Fiber Bragg grating sensing system is built in the experiment.The complex vibration wave generated by impact energy is processed by using the envelope of peak value in MATLAB.The experimental results show that when the impact energy is stronger,using the time length corresponding to the peak attenuation of 10% as the demodulation basis has a nice goodness of fit.The linear fitness of acrylic plate and aluminium plate is 0.94 and 0.89 respectively.At the same time,it is concluded that this method can be used to preliminarily determine whether the plate is viscoelastic or not.This is a new potential demodulation method based on fiber Bragg grating for practical engineering impact energy detection.